1. Field of the Invention
The present invention relates to an apparatus and method for controlling an operation of a linear compressor, and more particularly, to an apparatus and method for controlling an operation of a linear compressor in which a work operation value is obtained by using a current and a voltage and a stroke is controlled with a variation amount of a size of the work operation value.
2. Description of the Background Art
In general, a compressor serves to heighten a pressure of a coolant vapor (that is, to compress the vapor) so that the coolant vapor evaporated from an evaporator can be easily condensed.
According to the operation of the compressor, the coolant is repeatedly condensed and evaporated, circulating in a freezing device, to carry heat from a cold place to a warm place.
These days, there are various types compressors are in use, of which a reciprocating compressor is the most widely used.
The reciprocating compressor uses a method in which vapor is compressed by a piston which moved vertically within a cylinder to thereby heighten a pressure. In addition, since a compression ratio can be varied by varying a stroke voltage applied to the reciprocating compressor, the reciprocating compressor can be also used to control a variable cooling force.
However, the reciprocating compressor is to compress vapor by changing a rotational movement of a motor to a linear movement, for which, thus, a mechanic converting device, such as a screw, a chain, a gear system or a timing belt, is requisite for converting the rotational movement to the linear movement.
Thus, its energy conversion loss is great and the structure of the device is complicate, so that, recently, a linear compressor adopting a linear method allowing a motor itself to make a linear movement is favorably used.
The linear compressor has advantages that, since the motor itself directly generates a linear driving force, it does not need a mechanical conversion device, and thus, its structure is not complicate and a loss due to an energy conversion can be reduced.
In addition, since there is no connection region where friction and abrasion are inevitably generated, its noise can be much reduced.
Moreover, in case that the linear compressor is used for a refrigerator or an air-conditioner, since the compression ratio can be varied by varying a stroke voltage applied to the linear compressor, the linear compressor can be used to control a variable cooling force.
FIG. 1 is a schematic block diagram showing the construction of an apparatus for controlling an operation of a general linear compressor.
As shown in FIG. 1, an apparatus for controlling an operation of a linear compressor includes: a linear compressor 3 for varying a stroke (a distance between a top dead center and a bottom dead center) according to a reciprocal movement of a piston by a stroke voltage, to thereby control a cooling force (a freezing capacity); a current detecting unit 4 for detecting a current applied to the linear compressor 3 according to a stroke variation; a voltage detecting unit 5 for detecting a voltage generated at the linear compressor 3 by a stroke variation; a microcomputer 6 for computing a stroke by using the current and the voltage detected by the current detecting unit 4 and the voltage detecting unit 5, comparing the computed stroke with a stroke command value as inputted by a user and outputting a switching control signal; and an electric circuit unit 1 for switching an AC power with a traic 2 according to the outputted switching control signal and applying a stroke voltage to the linear compressor 3.
The control operation of the linear compressor constructed as described above will now be explained.
First, the electric circuit unit 1 outputs a stroke voltage according to a stroke command value as set by the user, and controls a cooling force of the linear compressor 3 as the piston performs a reciprocal movement according to the stroke voltage and the stroke (the distance between the top dead center and the bottom dead center of the piston) is varied.
That is, the linear compressor 3 controls the cooling force in such a manner that the stroke is varied according to the reciprocal movement of the piston within the cylinder and the cooling gas inside the cylinder is discharged through a discharge valve to a condenser.
When the stroke is varied according to the stroke voltage, the current detecting unit 4 and the voltage detecting unit 5 detect a voltage and a current generated from the linear compressor 3, respectively, and the microcomputer 6 computes the stroke with the detected voltage and the current.
If the computed stroke is smaller than a stroke command value, the microcomputer 5 outputs a switching control signal which renders an ON period of the traic to be lengthened, to thereby increase the stroke voltage applied to the linear compressor 3.
If, however, the computed stroke is greater than a stroke command value, the microcomputer 6 outputs a switching control signal for rendering the ON period of the traic to be shortened, to thereby reduce the stroke voltage applied to the compressor 3.
However, the conventional apparatus for controlling an operation of a linear compressor has a non-linearity having a severe mechanical movement characteristic. Thus, without considering the non-linearity, a precise controlling is not possible with the linear control method.
Therefore, an object of the present invention is to provide an apparatus and method for controlling an operation of a linear compressor that are capable of controlling a top dead center (TDC) of a piston in consideration of an error according to a non-linear characteristic by obtaining a work operation value by using a current and a voltage and controlling a stroke with a variation amount of a size of the work operation value, and thereby improving an operation efficiency of the linear compressor.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described herein, there is provided an apparatus for controlling an operation of a linear compressor comprising: a sensorless circuit unit for detecting a current and a voltage applied to a linear compressor and outputting a work operation value corresponding to them; a stroke controller for receiving the work operation value and outputting a switching control signal according to a variation amount of the work operation value; and an electric circuit unit for receiving the switching control signal from the stroke controller and outputting a certain voltage to the linear compressor.
To achieve the above objects, there is further provided a method for controlling an operation of a linear compressor including the steps: inputting a stroke command value by a user; detecting a current and a voltage generated when the linear compressor is driven according to the stroke voltage; detecting a work operation value with the detected current and voltage; receiving the work operation value and comparing it with a previous work operation value; outputting a switching control signal if a variation amount of the compared work operation values satisfies a predetermined value; and switching an AC power with a traic according to the switching signal, applying the stroke voltage to the linear compressor, and driving the compressor.